04. The Trigeminal System

1. 04. The Trigeminal System Somatic Sensation of the Face and Head

2. Objectives: • Outline the two pathways for facial sensation from the head. • Contrast facial sensation from the head and somatic sensation from the body. In what ways are they similar? Different? Try drawing this on the Haines atlas diagram at the end of the lecture. • Diagram the corneal reflex: the afferent and efferent limbs as well as nuclei involved in the brainstem. • If a person does not blink, how would you determine if the problem were in the sensory (afferent) limb, motor (efferent) limb, or brainstem interconnections for the corneal reflex? • Explain how a single, small medullary vascular lesion could abolish pain and temperature from the face on the right side and pain and temperature from the body on the left side. What vessel is most likely occluded?

3. Peripheral Receptors and Sensation • Structures served by trigeminal system CN V-1 CN V-2 ? Great auricular nerve (C2-C3) CN V-3

4. How many neurons in sensory pathway? • DCML/ALS • Peripheral ganglion (DRG) • Spinal cord, medulla • VPL nucleus of the thalamus • Trigeminal system • Peripheral ganglion (Trig. gang.) • 2 nuclei in brainstem (pons, medulla, sp cord) • VPM nucleus of the thalamus

5. Primary Sensory Neurons: Trigeminal ganglion CN V-1 CN V-2 Trigeminal ganglion CN V-3

6. Primary Sensory Neurons: Trigeminal ganglion CN V-1 CN V-2 CN V-3 Primary sensory neuron

7. Second-Order Trigeminal Neurons • Originate in two brain stem nuclei: • Principal (chief) trigeminal nucleus • Spinal (descending) trigeminal nucleus Young, Young and Tolbert, 2008 Fig 11-10 

8. III. Second-Order Trigeminal Neurons • A. Principal (chief) trigeminal nucleus • Mediates fine touch, joint position, vibration. • Located in pons lateral to motor nucleus of CN V. • This would be equivalent to what nucleus of the brainstem? _____________ Young, Young and Tolbert, 2008 Fig 11-10 

9. III. Second-Order Trigeminal Neurons • B. Spinal (descending) trigeminal nucleus • Mediates pain and temperature. • Spinal (descending) trigeminal tract • Descends caudally as far as C2-C3 and is continuous with dorsal horn. • This would be equivalent to what region in the spinal cord? _____________ Young, Young and Tolbert, 2008 Fig 11-10 

10. III. Second-Order Trigeminal Neurons • C. Ascending Trigeminal Pathways • Axons of second-order neurons form the trigeminothalamic pathway to the VPM nucleus of the thalamus. • Axons from neurons in the chief sensory nucleus carry sensations such as: _____ • Axons from neurons in the spinal trigeminal nucleus carry sensations such as: ____ Secondary sensory neuron Secondary sensory neuron Young, Young and Tolbert, 2008 Fig 11-10 

11. IV. Third Order Neurons • Project from VPM in the thalamus to the Postcentral gyrus (primary sensory cortex) • Axons course through the internal capsule

12. V. Primary Somatosensory Cortex, Postcentral Gyrus There are four different body maps to help extract texture, form, and motion that come from the head and body. Name them: 1. DCML (vibration, fine touch, proprioception) 2. ALS (pain, temperature) 3. Trigeminal system (vibration, fine touch) 4. Trigeminal system (pain, temperature)

13. VI. Association Somatosensory Cortex Posterior Superior Parietal Areas 5 and 7 of Brodmann.

14. Self-assessment: When you think you have mastered the pathways, select 2 colors in both a dark and light shade. Use the dark color for the body and the lighter color for the face pathways. e.g. Light blue-Trigeminothalamic (ventral) Dark blue – ALS Pink – trigeminothalamic (dorsal) from chief Red – DCML Animation